The use of very thin polarizing devices makes it possible to produce optical components without the need for expensive lens elements and more importantly, lessen alignment problems in order to maintain high light throughput. For any integrated device, the goal is to shorten the optical pathlength in order to decrease diffraction losses. These, and other aspects of vertical integration technology, as it is known, are described by Shiraishi et al., in Vertical Integration Technology for Fiber-Optic Circuit, OPTOELECTRONICS, Vol. 10, No. 1, pp. 55-74, March 1995.
The closest product of which we are aware, for producing optical isolators of the kind described herein is POLARCOR™, a high quality finished optical component available from Corning Incorporated, Corning, N.Y. This product is available in planar shapes with dimension up to 30 mm parallel to the major principal transmission direction.
POLARCOR™ products are also available in thickness as low as 0.2 mm.
In addition to POLARCOR™, we are aware of a several patents such as U.S. Pat. Nos. 5,430,573; 5,322,819; 5,300,465; 5,281,562; 5,275,979; 5,045,509; 4,792,535; 4,479,819; JP 4-279337; JP 5-208844; and EP 0 719 741 all of which have described glass articles which are polarizing in the infrared region.
JP 4-279337; JP 5-208844 describe a copper-based polarizing glass which, according to the patent application can measure less than 240μ in thickness. However, the examples were limited to glass thickness in the range of 100 to 1000μ, The polarizing glass of this patent application was prepared by polishing stretched copper halide-containing glass to a thickness in the range of 100 to 1000μ, and then subjecting the glass to a hydrogen atmosphere to form polarizing glass.
One disadvantage of the methods described in the above references, at least with respect to making ultra-thin polarizing glass, is the difficulty of handling and processing very thin free-standing glass pieces as required in the instant invention. In this connection, JP[Hei]9-86956 suggests a method for reducing loss due to the high stress used for stretching small crystals embedded in a glass matrix. However, there continues to be a need for improvements in the processes for making thin glass polarizers.
Accordingly, it is the object of the present invention to provide approaches for making ultra-thin polarizing glass articles in which the above difficulties are reduced or eliminated.